The present invention relates to pen plotter and pen type indentification systems associated therewith and, more particularly, to a pen type sensor for use in a graphics pen plotter wherein plotter pens are moved along a pre-established path between a pen holding area and a plotting area for reading a plurality of vertically oriented reflective indicia positions thereon to create a logic output signal representative of the pen type comprising, a hollow body member having a pair of angled front surfaces; means associated with one of the pair of angled front surfaces for directing a light beam to simultaneously strike the indicia positions at a point on the path of pen movement; a plurality of detector means associated with the other of the pair of angled front surfaces for receiving on respective sensing surfaces thereof the light beam as it is reflected by reflective indicia on a pen at respective ones of the positions and for creating respective bi-stable output signals reflecting the presence and absense of reflected light on the sensing surfaces; and, means for reading the output signals from the detector means as the logic output signal as pens pass the point on the path.
Modern pen plotters employ a variety of types of pens therein requiring different pen speeds, pen pressures, etc., to create optimum line quality. As a very basic approach, one can provide the plotter with such information prior to the beginning of a plot where a single type of pen is to be employed. Most quality, production grade, commercial plotters, however, employ a multitude of pens even within a single plot for purposes of changing color, line width and the like. Accordingly, it is known in the art to provide each pen with readable indicia so that the pen type can be dynamically determined during the plotting process.
A typical prior art approach to the determination of pen types is shown in FIGS. 1-4. The cylindrical plastic body 10 of each pen 12 is provided with a plurality of strips 14 of reflective tape in a pre-established configuration for each pen type. A sensor system, generally indicated as 16, is used to vertically scan the strips 14 on each pen 12 to determine the pen type. Sensor system 16 comprises a light beam source 18 and a light detector 20 mounted to a moving member 22 so that light 24 striking a strip 14 of reflective tape will be reflected to the light detector 20 to produce a signal on the wires 26. Typically, the source 18 and detector 20 employ modern diode technology; that is, there is a light-emitting diode (LED) within the light beam source 18 and a photo transistor within the light detector 20. The moving member 22 is scanned vertically across the strips 14 as indicated by the arrow 28 by an appropriate mechanism (not shown). Alternatively, of course, the pen 12 could be moved vertically across a stationary sensor to achieve the same results. As those skilled in the art will recognize, if four strips 14 of reflective tape are present at four associated positions on the body 10 of pen 12, the output from the sensor system 16 on wires 26 will be a binary 15, i.e., "1111". By eliminating various ones of the strips 14, the other fifteen possible combinations of four binary bits (i.e., 0000-1110) can be produced. More or less strip positions can, of course, be used as desired for fewer or greater possible numerical designations of type.
The critical portions of interest of a modern pen plotter employing a carousel 30 for holding a plurality of pens is shown in FIG. 4. A pen holder 32 moves back and forth along beam 34 within the plotting area 36 when actively plotting. To pick up or change a pen 12, the pen holder 32 moves from the plotting area 36 off station to the carousel 30 as indicated by the dotted arrow 38. To sense pen type, the carousel 30 must be rotated as indicated by the arrows 40 to first position the desired pen 12 adjacent the sensor system 16 wherein it is vertically scanned by sensor system 16 as described above. The carousel 30 is then rotated to place the pen 12 at the pickup position to be picked up by the pen holder 32. As can be appreciated, this is a two-step operation requiring both time and associated logic within the plotting system to accomplish it. Additionally, the sensor system 16 as described above is relatively complex and parts intensive in order to be able to properly vertically scan the strips 14 in the manner previously described.
Wherefore, it is the object of the present invention to provide a pen plotter pen type identification system which is simple in constructions, does not require a scanning mechanism associated therewith, and which can dynamically scan a pen without the requirement of the pen being moved to a separate sensing location.
It is another object of the present invention to provide a pen plotter pen type identification system which produces output sensing with discrete TTL switching signal levels.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter taken in conjunction with the drawings which accompany it.